Sure, the lower the temperature is the longer life time there is, but are we talking about 10 to 15 years? With 70-80% power drain, the efficiency of PSU X with Bronze marking will be the highest.
RAMs cost 17€ / 4 Gb (try to read). Nobody has said this build was to be overclocked, I just used the OC to speak about peak power consumptions.
I'll be picking Samsung F3 1 TB as the main HDD from a Finnish shop - forgot to mention, using it as storage for media. 64 Gb should be large enough SSD to hold 64-bit OS + 1-2 games?
Anyhow, I'll probably take either HCG 620 / XFX 550.